1. Field of the Invention and Prior Art
The invention relates to high-density foams and foam composites and is particularly directed to rigid polyurethane/polyvinyl ester foamed polymer hybrids comprising a particular type of hydroxyvinyl ester, the foam ingredients all together providing the necessary components for a hybrid polyurethanepolyvinyl ester matrix, having a density of at least 20 pounds per cubic foot, and composites comprising the same.
Rigid polyurethane and isocyanurate-modified polyurethane foams have been variously described in literature, both in patent and scientific papers by various authors. Almost all of these isocyanate-based foams containing various fillers were primarily produced by two methods, and almost all of them were intended for insulation purposes. They have been produced either continuously for low-density (2-3 pcf) thermal insulation (board stock) or by molding of panels. Various equipment has also been designed for that purpose.
However, very little has been disclosed in literature or patents regarding high-density, rigid polyurethane or modified polyurethane foams designed for structural purposes and having strength properties comparable to wood, although a number of molding methods including reinforced reaction molding (RRIM) have been developed for the production of molded parts, especially for the automotive, furniture and appliance industries.
An object of this invention is the intermittent or continuous production of high-density foams comprising a special hybrid of polyurethane/polyvinyl ester foam comprising a particular type of hydroxyvinyl ester, especially in combination with various fillers and reinforcing fibers, which are uniquely designed to provide a combination of mechanical strength properties and environmental (outdoor weathering) properties which make them eminently suitable for applications where wood is normally used for strength and durability. Wood substitutes made of reinforced high-density fiberglass-reinforced polyurethane foams have heretofore been prepared, for example, a product known as Centrite, and a number of like products described in Industrial And Engineering Chemistry, Product Research And Development, Vol. 23, No. 1, (1984) p.p. 81-85, by Kiyotake Morimoto and Toshio Suzuki, and in Proceedings, SPI International Urethane Conference, Strasbourg, France, June 9-13, 1980, by F. Okagawa et al., pp. 453-467. Reference is also made to our U.S. Pat. No. 4,680,214, issued July 14, 1987, which uses a different approach.
It is an object, therefore, to provide rigid foams and reinforced foam composites by a new approach, as above-identified, and thereby to provide such foams having advantageous characteristics such as improved impact strength and flexural modulus, especially of the final reinforced composites, and which therefore have not only the advantage of further superior properties, such as much better dimensional stability and improved weathering resistance as well as resistance to biological attack, but which can also be produced either by molding or continuously and, if desired, in dimensions beyond any possibilities as far as wood boards are concerned (in addition to absence of the many imperfections present in wood because of knots and splits) and to provide foams, the uniqueness of which lies also in the fact that, while resembling wood in many respects because of many physico-mechanical properties similar to wood, they can be used in applications where wood would not be practical or acceptable due to deterioration of the latter on aging.
Reinforced composite materials comprise a matrix material, such as a resin, and a reinforcing material such as fibers. Composites, therefore, are expected to be new structural materials for the automotive, building, ship, aircraft, and space industries. The resins for the matrix include both thermoplastic and thermosetting resins. Major thermoplastic resins include polypropylene and polyethylene terephthalate, and major thermosetting resins include polyurethanes, polyisocyanurates, polyureas, cyclopentadiene polymers, unsaturated polyester-urethane hybrid resins, and now polyurethane hydroxyvinyl ester hybrid resins.
Some of the most widely-used thermosetting composites for automative use comprise SMC (sheet molding compounds), which are used for hoods, front grill panels, and trunk lids for cars. Other widely-used thermosetting composites for automobiles are polyurethane and polyurea-based. These are used in the area of fascias, fenders, door panels and some indoor structural parts. Such composites comprise a resin and glass fibers. Other types of composites, e.g., plastic foam-based composites, are contemplated for use as wood substitutes comprising polyurethane foam and glass fibers. (International Progress in Urethanes, Vol. 2, page 85 (1980), Edited by K. Ashida & K. C. Frisch and published by Technomic Publishing Co. Inc.).
Polyurethane foams are recognized to be excellent materials, that is, readily processed, having a high degree of chemical resistance, and being susceptible to a broad-variety of molecular designs varying from flexible foams to rigid foams and from low density to high density foams.
These advantages are exploited in the production of urethane foam composites by means of combinations of rigid urethane foam and glass fibers, and the products are applied as wood substitutes and light-weight structural parts in industry. Such products are available in the USA (Centrite.TM., Center Corp.) and in Japan (Neo-Lumber, Sekisui Chem., and Airlite FRU, Nisshinbo Ind.).
However, existing composites have numerous disadvantages, resulting in limited use. The disadvantages include: (a) excessive coefficient of thermal expansion, (b) poor dimensional stability, (c) poor temperature stability, and (d) viscosity problems for making mat molding or fiber-reinforced composites due to relatively high viscosity of the systems.
In an effort to solve these disadvantages, a relatively new concept, that is, the concept of polymer hybridizing, was applied according to the present invention. Polymer hybridizing involves multicomponent polymer systems, comprising at least two different polymer networks. In the present case, the different systems involved are polyurethane and vinyl ester comprising a particular type of hydroxyvinyl ester, designated by Formula I in the following, which "interpenetrates" into both the polyurethane and the polyvinyl system.